Deflection yoke



June 7, 1960 G. L. lRvlNE ET AL DEFLECTION YOKE Filed Oct. 16, 1957 Fatented June 7, 196

DEFLECTION YOKE Gordon L. Irvine, Cooksville, Ontario, and Gerda Voss,

Toronto, Ontario, Canada, assign'ors to Canadian Admiral Corporation, Ltd., Port Credit, Ontario, Canada Filed Oct. 16, 1957, Ser. No. 690,493

7 Claims. (Cl. 313-76) This invention relates to improvements in television receivers and more particularly to a method and apparatus for controlling the linearity and width of the picture or raster produced by the defiected beam in the picture tube.

As is well known to those versed in the art, the electron beam of a cathode ray picture tube is defiected horizontally and vertically in synchronous relation to each other to provide a raster of a predetermined height and width.

The height of the picture is Controlled by a Vertical deflection circuit and the width of the picture by a horizontal deflection circuit. The beam is more commonly deflected in two ways, either by electrostatic deflection or by magnetic deflection. Magnetic deflection is provided by coils which are disposed alongside the neck of the tube in such a position that current in the Vertical coils cause the beam to be deflected vertically and current in the horizontal coils cause the beam to be deflected horizontally. 'I-'he Vertical beam is defiected at the rate of 60 cycles per second and the horizontal beam is deflected at the |rate of 15,750 cycles per second. Both -of said coils which control the beam effect a control through currents that are produced in the coils derived from the Vertical and horizontal sweep crcuits.

In connection With the horizontal deflection coils, it is common to have the current through the coils increase to a predetermined amount and then decrease suddenly by use of some form of oscillator, held in step by the synchronization signals from the station. The amplitude of the current in the horizontal amplifier determines the width or amount of deflection of the beam and the shape of the wave form of current in the output of the horizontal amplifier determine the manner in which the beam is deflected across the face of the tube. The manner in which the beam is defiected across the face of the tube is commonly characterized by the term "lnearity. A beam deflected at a constant rate has a good linearity whereas a beam deflected at a rate which varies as it traverses the tube has poor linearity. Usually the manufacturer strives to generate a wave form in the horizontal amplifier that is of a saw-tooth variety, with the rising portion of the curve linear. Since the first portion of the rising curve is usually realized from the back voltage produced by the damper tube and the remainder of the curve by the horizontal output tube and the two combined to provide a saw-tooth wave, circuit control means is usually provided to enable the shape of the beam, within certain limits, to be controlled in order to correct for nonlinearity due to circuit and tube tolerances and limitations.

Usually the above has been etfected by providing a width and a linearity control each of which may be adjusted to provide the proper width and the best degree of linearity in the final stages of production.

There is a disadvantage in having these controls however because the controls are usually in the form of a potentiometer or adjustable coils and are expensive as well as requiring more ltime for installation. Another important disadvantage resides in the fact that these con'- trols are available for adjustment by unauthon'zed persons who, not being qualified to make such adjustments, tamper with the same and cause a resultant deterioration of the picture which they attribute to the manufacture of the set rather than the fact that they have tampered with the set. It is therefore desirable, to eliminate all except the most essential conrols, to not only cheapen the cost' of the receiver but to prevent persons with inexperience from tampering with the controls and spoiling the fidelity of the picture. It has been found that in the horizontal circuit it is particularly possible -to eliminate the linearity and width controls. One of the problems however,A has been to provide the proper lineari'ty without atfectng the width to the detriment 'of 4the set.

In the present invention, it is possible to improve the linearity by control means disposed within the yokc, without causing a serious deterioration of the width.

Briefly, it comprises a means for insertion in the flux field of the horizontal coils such that eddy currents are: set up within the device, acting in opposition to the fiux of the field, to improve the linearity and or 'control the width.

In the drawing, the figure of the drawing shows a view of a yoke for a television receiver wherein certain portions have been broken away and shown iu section to more clearly depict the invention.

As can be seen from the drawing, there is provided af horizontal deflection winding 10 which, in this case, consists of a pair of skein-like coils, the upper portion end of each being shaped with an outward slant-adapted to engage with the bell of the picture tube. The upper end connects with a pair of longitudinally extending flat runs 11 disposed alongside the neck of the tube and connected by a lower loop 12. There is a pair vof such coils, each coil of the pair being disposed'upon opposite sides of the'` neck of the tube with the runs 11 of the opposite coils being adjacent t-o each other and on one side of the tube' and the other opposing runs being'on the opposite side of the tube and adjacent to each other. inner faces of these coils are formed to an arcuate form so that they mayl be brought into close proximity to the' 'neck of the tube and hence the gun, thus exercising the greatest effect upon the electron beam.

Likewise, .the Vertical coils comprise thel outwardly shaped upper ends 15, the horizontal runs 16 and the lower connecting portions 17. TheA ends of the Vertical coils are disposed inwardly of the horizontal coils. The runs extending along the neck of the tube. of the opposite coils are adjacent to each other and disposed inwardly of the opposite runs of a single coil of the horzontal wind-v ing. Usually a suitable form indicated at 20 is provided' for holding the coils in position and a terminal ring 21f is also provided having lugs 22 to which the wires 23 leadj ing to the coils may be secured. A highly permeable material, which may be called a core, surrounds the straight portions of the coils and may comprise four segments 30 of ferro-magnetic material, a number of which f are on the market and well known 'to those versed in'the art. vThis material provides 'an annular flux path around the coils and'is preferably of 'a material not subject to Permanent magnetization but having a high permeability in order that the effective inductance of the coils may be increased and a flux path be provided exteriorly of the i coils to prevent extraneous magnetic radiation and to concentrate the flux.path interiorly of the yoke. The above construction is well known to those versed in the art.

As previously stated, the horizont'al coils conduct what is commonly known as the saw-toothed current waveI the shape of which is Controlled largely by the circuitry lof the horizontal oscillator and amplifier and its asso- The removal of the `Ywidth'aud2 ciated components.

Preferably, the

7 3 linearity controls with the attempt at simplification, has reulted in a horizontal defiection system which is characterized by some degree of inherent non-linearity which is observed as a stretehing ofV the raster or picture near the beginning of vthe horiohtal scan and a crowding or compression near the end of the scan. V

It has been found however, that by this ihvention the lnearitiy may be gre'atly'improved by providing a vmaterial which is inserted between the core and the coil at a point lwhere it 'has an effect upon the horizontal coils but no effect uponlthe vertical coils. One means for accomplishing this effect comprises the provision of a Sheet cfaluminum foil 40 having a width less than the core 30 and a length approximately equal to the space between the horizontal runs of one of the horizontal defiection coils and placed opposite'" to what would normally be considered the opening in one of the dellection cons.

lt is appreciated that width alone has previously been Controlled by the use of a cylindrical sleeve which could be inserted' between lthe neck of the tube and the coil winclings and adjustableV inwardly, and outwardly to control the width. The sleeve of the prior art, howe'vcr was o-f little practical use in controlling linearity because When it was placed within the coil far enough to haveV any control on the linearity it decreased the width of the picare beam to such an extent that it was a useless ertpedient. Fur'therm'ore, this previous control was in a position'wh'ere it could be tarnpered Vwithv by unauthorized persons, and being within the field was subject to the accumulation of an electrostatic charge, making it necessary to ground' the Shield, otherwise the person touching it would obtain a shock. The present Shield is supported around the core upon a piece of tape 41 Vof insulating character and,v once the proper size is determined by ei'tperimentation, may be placed in position for a cornplete run 'of television receiver's being held in place by 4. insertion of tubes through the yolie and enables a yoke to be used wherein the runs of the coil may be placed closer to the ueck of the tube;` A metallic member placed next to the neck of the tube requires additional space and additional insulation to prevent shorting of the coils.

Having thus described our invention in an embodiment thereof, we are aware that numerous -and extensive departures may be made therefrom without departng from the spirit or scope of the app'ended claims.

l. A defiection yoke for defiec'ting the 'electron beam of a cathode ray tube comprising pair of horizontal and Vertical beam deilectingv coils, each of said pairs of coils comprising a pair of inductive windings, each of which is disposed on diametrically opposite sides of the yoke, and eachof said pairs being displaced 90 relative to the other, field controlling means for the horizontal defiection coils comprising a conductive non-magnetic eddy v current producing device `disposed within the field of the the magnetic core 30 which being of the segmental variety is usually held in place by a clamp 42 in a manner well known in the art. The material may be very thin and may be of any lnon-magnetic material such as aluminum, copper or bra'ss.

The improvement in the linearity ofthe horizontal scan is effected partly in directly modifying the deflec'tio'n field and partly in modifying the defiection current. Eddy currents and their result'ant oppo'sing magnetic fields are set up in the' conducting material which are proportional to the rate of change of the field producing them.v This tends to equalize the effects of a non-linear deficction current- Also losses introduced by these eddy currents tend to affect the fi'rstihalf of the horizontal scan more than the last half of the scan because of the difference in source i-rnpedances of the two circuits producing the respective deflection currents. It is appai'ent however that other theories of operation than the one presentlyconsideredmay later be evolved without effcctig the results reali'zed which, as stated, are toprovide an improvement in the linearity without decreasing thewidtli, as is common in: the prior art.

We have found that the best results are obtained by a inglepiece of aluminum foil disposed as stated. However, good results can also be obtained by more than one piece of aluminum foil properly placed to control tliefluxV in the manner described. Since aluminum foil in. this instance is operated in conjunction with or against the higher frequency of the horizontal deflection yoke where it is effective, it has little o r no effect upon the Vertical coil which is Operating at 60 cycles. In addit'ion, it is'disposed'opposite to adjacent runs of opposite Verticl' deflection coils;

Plairigtlie control within the yoke as stated, enables it 'to be adjus'te'd during 4the .manufacture of the device acf-puts. it out of. the 'way of subsequent tarnpering by utfior'ized persons;v In addition, by placingfit in the positinhwnrit 4camot be darnaged by the removal or horizontal defiection coils.

2. A defiection yoke for use in conjunction with the dcilection of the electron beam in a cathode ray picture tube or the like comprising pairs ofvertical and horizontal deection coils, each pair of coils comprising an inductive winding, and each coil of each pair including longitudina'lly extending portions arr-anged to extend alongside the neck of a picture tube, and wherein the longitudinal -portions of one of said horizontal coils are disposed adjacent to the respective longitudinal portions of the other of said horizontal coils ontthe opposite side of said tube neck with the longitudinal portions of the Vertical coilsv interposed between those of the horizontal coils, magnetically permeable means for said parts of said coils surrounding the coils and providing a low permeability path, means for controlling the ,magnetic fiux produced by the horizontal defiection coils to determine the effective linearity and width of the raster or picture produced by the cathode ray being Controlled ccmprising conductive non-magnetic rneans reactive'to the flux produced in the horizontal winding for' con trolling the linearity without material reduction in the width of the beam.

3."A deflectionV yoke as described in claim 2, wherein said last mentioned means comprises a non-magnetic metallic layer disposed between the windings and the magnetically permeable means.

4. A dellection yoke as describedin clairn 2, wherein said last mentioned means comprises a sheet of nonmagnetic conductive material capable'of producing eddy currents acting in opposition to change in the ux generated by the horizontal coils.

5. A defiection yoke as described 111 claim 2, wherein said last mentioned meansA comprises a sheet of conductive non-magnetic metal of less width and vlength than the opening in the horizontal coil and ,wherein' said'sheet of metal is disposed in a fiux controlling position for at least one of said horizontal coils.

6; A defiection device as described in claim 2, wherein` said last mentioned means comprises a sheet of thin nonmagnetic metal foil and wherein Vsaid Sheet of foilis disposedV in the magnetic field of the horizontal clefiection References Cited in the file ofthis patent UNITEDSTATES PATENTs schisifiger' July 31; i Scull" Sept. 25 19,151 Fernsler Mar."22, 1955 

